Turkey is negotiating alternatives to the U.S. F-16 fighter jets, the U.S. is not the only option for Ankara, President Tayyip Erdogan said.

"At the moment, the opinion of the (U.S. president's) administration is developing in a positive direction. Of course, America is not the only way out for us. If necessary, as with the S-400 systems, we are negotiating with alternatives outside the United States...We have alternatives," Erdogan told reporters on the plane on his return from Azerbaijan.

The U.S. had earlier issued a formal notice to Turkey to exclude it from its program of supplying the latest F-35 fighter jets because of Ankara's purchase of Russian S-400 air defense systems. Washington canceled a joint memorandum on the F-35 with Turkey, signing it with the seven remaining partners in the F-35 project - Britain, Italy, the Netherlands, Australia, Denmark, Canada and Norway. Erdogan subsequently announced a U.S. offer to buy other fighters, but not the fifth but the fourth generation F-16s. The issue needs to be negotiated in the U.S. Congress - the State Department is lobbying for it, convincing congressmen that the deal "serves the interests of Washington."